This invention relates to ink drop or ink jet printers of the type wherein drops are continuously produced from a continuous stream of liquid emitted under pressure from a nozzle and selected drops are charged and electrostatically deflected between paths intersecting either a target or a gutter. More specifically, this invention relates to ink supply apparatus for such printers having means for degassing the liquid. By degassing is meant the removal of gas bubbles from a liquid ink or the prevention of the generation of gas bubbles in a liquid ink.
Continuous drop printers of the present type are adversely affected by gas bubbles in the ink. For example, the gas bubbles change the nature of the sonic stimulation of the liquid. The sonic stimulation is used to promote uniform drop shape, space between drops and point of drop formation. A piezoelectric transducer coupled to a manifold housing the ink is one device for sonically stimulating the ink. Gas bubbles are also the source of other undesired effects in the printer system.
Accordingly, it is a main object of this invention to suppress the formation of gas bubbles in the ink of an ink jet printer.
Another object of this invention is to rid the ink in the manifold of a drop generator and in the ink supply of gas bubbles to obtain improved print operation.
The above and other objects of this invention are achieved by degassing the ink suply for the printer. Two means for degassing are used separately or jointly. One means is to reduce the gas pressure adjacent the ink in the ink supply vessel. The second means is to heat the ink in the ink vessel. A principal cause for the generation of gas bubbles is the change in pressure in the drop generator manifold when the continuous drop stream is turned off. The pressure falls from a high operation level to a low ambient pressure level. Gases dissolved in the liquid at the high pressure are released at the lower pressure.
In this invention, the ink supply that feeds the manifold is processed to reduce the quantity of gas dissolved in the ink. As stated, this is achieved by reducing the gas pressure above the ink, by heating the ink or by a combination of the two techniques.